Magnetic refrigeration is, in principle, a much more efficient technology than conventional vapor compression refrigeration technology as it is a reversible process and, moreover, it does not use environmentally unfriendly ozone-depleting chlorofluorocarbon refrigerants (CFCs). Magnetic refrigeration depends on the magnetocaloric effect (MCE), utilizing the entropy of magnetic spin alignment for the transfer of heat between reservoirs.
Since the late nineties, the use of a Gd5Ge2Si2 compound in near-room temperature magnetic refrigeration applications has attracted attention owing to its potential as a suitable refrigerant material for near room temperature magnetic refrigeration. A large magnetocaloric effect in the Gd5Ge2Si2 compound in the 270-300 K temperature range has been reported by Gschneidner, Pecharsky and their coworkers in the following published references: Pecharsky, V. K. & Gschneidner, K. A., Jr., “The Giant Magnetocaloric Effect in Gd5(Ge2Si2)”, Phys. Rev. Lett. 78, 4494-4497 (1997); Pecharsky, A. O., Gschneidner, K. A., Jr., “The Giant Magnetocaloric Effect of Optimally Prepared Gd5Si2Ge2”, J. Appl. Phys. 93, 4722-4728 (2003), and Pecharsky, V. K. & Gschneidner, K. A., Jr., “The Giant Magnetocaloric Effect in Gd5(SixGe1-x)4 Materials for Magnetic Refrigeration”, Advances in Cryogenic Engineering, 43, edited by P. Kittel, Plenum Press, New York, 1729-1736 (1998).
The aforementioned references disclosed that the large magnetocaloric effect observed in the Gd5Ge2Si2 compound, in the 270-320 K temperature range, is the result of a magnetic field-induced crystallographic phase change from the high-temperature paramagnetic monoclinic phase to the low-temperature ferromagnetic orthorhombic phase. Unfortunately, large hysteresis losses were also observed in the Gd5Ge2Si2 magnetic refrigerant compound in the 270-320 K temperature range. These large hysteretic losses occurred at the same temperature range where the compound exhibits a pronounced magnetocaloric effect, referred as “The giant magnetocaloric effect”.
Choe, W. et al, and other researchers have proposed that the large magnetocaloric effect is the result of a field-induced crystallographic phase change from the high temperature paramagnetic monoclinic phase to the low-temperature ferromagnetic orthorhombic phase (see Choe, W. et al, “Making and Breaking Covalent Bonds across the Magnetic Transition in the Giant Magnetocaloric Material Gd5(Si2Ge2)”, Phys. Rev. Lett. 84, 4617-4620 (2000); Pecharsky, V. K. & Gschneidner, K. A., Jr., “Phase relationship and crystallography in pseudobinary system Gd5Si4—Gd5Ge4”, J. Alloys and Comp. 260, 98-106 (1997); and Pecharsky, V. K., Pecharsky, A. O., and Gschneidner, K. A., Jr., “Uncovering the structure-property relationships in R5(SixGe4-x) intermetallic phases”, J. Alloys and Comp. 344, 362-368 (2002)).
Other studies by Pecharsky et al and by other researchers have also observed the magnetocaloric effect of the Gd5Ge2Si2 magnetic refrigerant compound and the hysteresis losses behavior (See Pecharsky, V. K. & Gschneidner, K. A., Jr., “Tunable magnetic regenerator alloys with a giant magnetocaloric effect for magnetic refrigeration from ˜20 to ˜290 K”, Appl. Phys. Lett. 70, 3299-3301 (1997); Levin, E. M., Pecharsky, V. K., and Gschneidner, K. A., Jr., “Unusual magnetic behavior in G5(Si1.5Ge2.5) and Gd5(Si2Ge2)”, Phys. Rev. B 62, R14625-R14628 (2000); Giguere, A. et al., “Direct Measurement of the ‘Giant’ Adiabatic Temperature Change in Gd5Si2Ge2”, Phys. Rev. Left. 83, 2262-2265 (1999)).
There is a need to greatly reduce or eliminate the large hysteresis losses in the Gd5Ge2Si2 compound so that the potential of the compound as an efficient and attractive refrigerant material for near-room temperature magnetic refrigeration can be fully realized.
The embodiments disclosed herein therefore directly address the shortcomings of present Gd5Ge2Si2 magnetic refrigerant compounds, providing an alloy that is suitable for near-room temperature magnetic refrigeration applications.